Method of making a helically crimped continuous filament yarn

ABSTRACT

One side of a drawn homogeneous filament having at least 17 percent boiling water shrinkage is heated above its melting point while under high tension. The filament is then prebulked while under substantially no tension by being exposed to hot air at a temperature above the yarn glass transition temperature, soon after the initial heat treatment, and preferably before being wound. This produces a tighter crimp when the yarn is later subjected to hot water.

United States Patent 11 1 Self et a1. Nov. 6, 1973 METHOD OF MAKING AHEL ICALLY 3,457,613 7/1969 McClure 28/72.1 C IM E CONTINUOUS FILAMENTYARN 3,602,951 9/1971 Stanley 28/1.2

[75] Inventors: Joseph A. Self, B21101] Rouge La; FOREIGN PATENTS 0APPLCATIONS g z f g x i fzz' i'zk g ig z 1,064,765 4/1967 Great Britain28/13 '7 Court, N.C. Primar Examiner--Louis K. Rimrodt [73] AsslgneezMonsanto Company, St. Louls, Mo. Atmmgv Keny O Corley et aL [22] Filed:Feb. 22, 1972 [21] Appl. No.: 228,144 [57] ABSTRACT R l t 62 e 3 ed U sApphcatlon Data One side of a drawn homogeneous filament havlng at 1 ggg g g g 1968 least 17 percent boiling water shrinkage is heated aboveits melting point while under high tension. The filament is thenprebulked while under substantially no (g1. tension y being exposed tohot air at a temperature [58] Field 1 3 above the yarn glass transitiontemperature, soon after the initial heat treatment, and preferablybefore being wound. This produces a tighter crimp when the yarn is [56]References cued later subjected to hot water. 7

UNITED STATES PATENTS 12/1967 Daniel 28/12 2 Claims, 4 Drawing FiguresMETHOD OF MAKING A HELICALLY CRIMPED CONTINUOUS FILAMENT YARN This is adivision of application Ser. No. 772,766 filed Nov. 1, 1968, now U.S.Pat. No. 3,663,352, granted May 16, 1972.

11 The invention relates to a helically crimped continuous filamentyarn, and to a process for making such yarn. More particularly, theinvention relates to such yarn having an enhanced bulk level.

Numerous types of helically bulked or crimped yarn have been proposed inthe prior art, and are particularly useful when the yarn is to havesubstantial stretch. One such helically crimped yarn is produced byconjugate spinning, i.e., extruding two polymer components in parallelrelationship in a single filament. If the polymer components havedifferent shrinkages, the drawn filament will develop helical crimp whenheated. Conjugate spinning has a number of disadvantages, such as thenecessity for metering the two components to the spinneret orifices, andthe elaborate distribution passageways required for properlydistributing both polymer components to each orifice.

Another helically crimped yarn is produced by drawing a hot nonconjugateor homogeneous yarn while under tension over a sharp edge. In thisprocess-the edge produces a flattened surface on the yarn, whichflattened surface will be On the inside of the resulting helix when theyarn is bulked.

A further prior art process is disclosed in U.S. Pat. No. 3,226,792 toStarkie, wherein nylon 66 yarn is stretched, heated on one side to atemperature below the melting point of the yarn while being cooled onthe opposite side, and wound. The yarn is later unwound and immersed inboiling water to develop the bulk. When such a process is applied tonylon 66, the degree of bulk obtainable is limited because of therelatively small shrinkage of nylon 66.

Another approach is disclosed in U.S. Pat. No. 2,974,391 to Speakman,wherein one side ofa homogeneous filament is heated above the meltingpoint while the yarn is under a tension stretching the filaments notmore than percent of their length. The yarn is wound, and later unwoundand heated to develop the crimp.

According to the present invention, the drawn homogeneous yarn fed tothe texturing operation has a boiling water shrinkage (excluding theimmediate elastic recovery upon elimination of tension) in excess of 17percent. One side of the yarn is heated to a temperature above itsmelting point, while the opposite side of the yarn, is maintained below100 C., to impart latent bulk to the yarn. The yarn is then prebulked,i.e., subjected to a temperature above its glass transition temperaturewhile under minimum tension to crystallize the yarn in its bulkedconfiguration, preferably before the yarn is wound on a package. Theyarn is subsequently unwound and subjected to boiling water. The degreeof final bulk obtainable is considerably enhanced by the prebulkingstep, and is substantially higher than is attained by the prior art.

Accordingly, a primary object of the invention is to provide a helicallycrimped yarn.

A further object is to provide a yarn of the above character wherein thecrimps are in the form of a tightly coiled helix.

A further object is to provide a yarn wherein the ratio of the helixcoil length to the filament radius is less than 45.

A further object is to provide processes for making yarns of the abovecharacter.

Other objects will in part appear hereinafter and will in part beobvious from the following disclosure and the accompanying drawings,wherein:

FIG. 1 is a schematic perspective view of preferred apparatus forpracticing the invention;

FIG. 2 is a perspective view of a bulked filament according to theinvention;

FIG. 3 is an end view of the helix shown in FIG. 2, and,

FIG. 4 is a developed view of the helix shown in FIG. 2, illustratingthe relationships between the coil radius, the coil pitch, and coillength.

As schematically shown in FIG. 1, spun yarn 20 is withdrawn from package22 and fed to feed rolls 24 driven at a constant speed. Spun yarn 20next passes through a pigtail guide 26 and around draw pin 28. Yarn 20next passes in a plurality of wraps about draw roll 30 and itsassociated separator roll 32. A heated roll 34 contacts yarn 20 justbefore yarn 20 contacts draw roll 30 for the second time, for a purposeto be explained hereinafter. After leaving draw roll 30 for the lasttime, yarn 20 is fed by a pair of nip rolls 36 downwardly through aheated prebulking chamber 38 to a second pair of nip rolls 40. Uponleaving nip rolls 40, yarn 20 is taken up in an orderly fashion, as bythe illustrated conventional ring and twister assembly 42. With theexceptions of the temperature of roll 34, and the presence of rolls 36and 40 and chamber 38, the illustrated apparatus is identical to thatdisclosed in greater detail in U.S. Pat. No. 3,317,978 to McIntosh etal.

Referring more specifically to FIG. 1, yarn 20 is drawn by thecooperation of feed rolls 24, draw pin 28 and draw roll 30, as will beapparent to those skilled in the art. According to the presentinvention, roll 34 is heated to a temperature in excess of the meltingtemperature of yarn 20, and contacts and melts one side of the yarn. Thetemperature of the opposite side of the yarn is maintained below 100 C.,and preferably below C., by being contacted almost immediatelythereafter by draw roll 30. Yarn 20 at the time it is contacted by roll34 is under a tension in excess of 50 percent of the tension betweendraw pin 28 and draw roll 30. In the illustrated configuration, thetension on yarn 20 when contacted by roll 34 is substantially equal tothe tension of the yarn leaving draw pin 28. The temperature of roll 34is selected with respect to the yarn speed so that a small portion ofthe yarn periphery is melted, for example, a portion subtending an angleof about 30 at the filament center.

Yarn 20, being heated on one side by roll 34 and being cooled on itsopposite side by draw roll 30, is subjected to a severe thermalgradient. The surface contacted by roll 34 is melted, as noted above,and accordingly its crystalline structure is destroyed or disoriented.The probable states of the polymer across the the cross section from hotside to cold side are: (A) melted and disoriented, (B) disoriented, (C)oriented, crystalline and heat set, and (D) oriented and crystalline butnot heat set. To some depth, the heated side has little or no elasticrecovery after removal of the tension, and little or no shrinkage insubsequent relaxation treatments. The opposite side of the filament,however,

retains elastic recovery and shrinkage. Accordingly, when tension isremoved from the yarn, a helical crimp develops with the flattenedportion on the outside of the helix (see FIG. 2) due to the elasticrecovery difference across the filament. The direction of the helixrandomly reverses at short intervals along the filament. On treatmentwith a relaxing medium such as steam or boiling water, the crimpfrequency increases due to the shrinkage difference across the filament.

In womens seamless hosiery a crimp frequency of at least 27.5(preferably 30 or more) crimps per inch is desirable in order to obtainat least two crimps per knit stitch in the hose. This relationshipprovides good stretch and fit, and optimum stitch clarity. It has beenfound that in order to obtain 30 crimps per inch in the final productwhen using 15 drawn denier yarn, the untextured drawn yarn must possessa boiling water shrinkage of at least 17 percent, which requirementeliminates nylon 66 and nylon 6 (shrinkage about 11-12 percent) as asatisfactory polymer. When a 15 denier monofilament yarn with at least17 percent shrinkage is textured on roll 34 and then relaxed in boilingwater without passing through chamber 38, it will form a helical coilwith a radius R (see FIG. 3) of 0.15 to 0.21 millimeter. The crimpfrequency can be further increased according to the invention by passingthe yarn while under substantially zero tension through heating chamber38, wherein the yarn is subjected to a temperature higher than its glasstransition temperature to crystallize the filament while in its crimpedcondition, before the filament is exposed to boiling water.

As shown in FIGS. 2-4, the helix is characterized by the pitch P (thedistance between corresponding points on adjacent coils), the coilradius R as measured between the axis or center of the helix and thecenter of the filament, and the radius r of the filament. Thecircumference C of the cylinder on which the center of the filament liesis given by 2 1r R. As shown in FIG. 4, the length S of one completecoil equals \KZ'IrR) +1)". The helix angle a which the filament makeswith a plane perpendicular to the helical axis is equal to arctan P/2 1rR.

Prebulked filaments according to the present invention, after beingwithdrawn from the bobbin and relaxed two minutes in boiling water, arecharacterized by a ratio of S/r less than 45, and a coil length lessthan 0.924 millimeter. The ratio S/r takes account of the filamentdimensions, since it is more difficult to achieve a given helical radiusR and coil length S with, for example, a 15 denier filament than with asmaller filament such as one of only 2 or 3 denier. The ratio of(Rr/R+r) is within the range of 0.66 to 0.75.

EXAMPLE I Nylon 66 is spun as monofilament yarn and then drawn at a drawratio of 3.2 to a drawn denier of 15, passing under roll 34 at 1,800feet per minute. Roll 34 has a surface temperature of 280 C., which isabove the 262 C. melting point of this polymer. The yarn is then passedthrough prebulking chamber 38 and subjected to hot air at 265 C. for adistance of 10 inches. About pounds of air per hour are supplied at 5 p.s. i. g. to chamber 38. Nip rolls 40 are driven at one-half theperipheral velocity of rolls 36, to insure essentially zero tension onthe yarn during prebulking. A sample of this yarn withdrawn from thebobbin and relaxed in boiling water forms a helix with a radius R of0.146 millimeter, and a pitch P of 0.578 millimeter. This corresponds toa helical coil length S of 1.08 millimeter, or 23.4 helical crimps perinch of filament length along the helix. The ratio of S/r is 50.2. Thisyarn thus develops inadequate crimp for use in seamless hosiery as notedabove, since drawn nylon 66 yarn has a boiling water shrinkage of about11 percent.

Although this yarn is not suitable for seamless hose, the crimp isnoticeably enhanced by the prebulking treatment. The same yarn drawn andtreated by roll 34 under the conditions noted above, but not prebulkedby chamber 38, forms in boiling water a closely packed helix having aradius R of 0.26 millimeter. This corresponds to a length 5 of 1.63millimeter, or 15.6 crimps per inch. The prebulking step thus increasesthe number of crimps per inch by about 50 percent.

EXAMPLE II Nylon 66-610 copolymer (formed from mols hexamethylenediamine, 8O mols adipic acid, and 20 mols sebacic acid) is spun asmonofilament yarn and drawn at a draw ratio of 3.82 to a denier of 13.1.The yarn is passed under roll 34 at 1,275 feet per minute. Roll 34 ismaintained at a surface temperature of 262 C., as compared to thepolymer melting point of 240 C. The yarn is then passed throughprebulking chamber 38 and subjected to hot air at 235 C. for a distanceof 10 inches. About 1 9% pounds of air per hour are supplied at 3 p. s.i. g. to chamber 38. Nip rolls 40 are driven at one-third the speed ofrolls 36. A sample of this yarn withdrawn from the bobbin and relaxed inboiling water forms a helix with a radius R of 0.122 millimeter and apitch P of 0.358 millimeter. This corresponds to a helical coil length Sof 0.847 millimeter, or 29.9 helical crimps per inch of filamentmeasured along the helix. The ratio of S/r is 42.3. The boiling watershrinkage of this polymer is about 19 percent.

Seamless hosiery knit from the resulting yarn has ex cellent appearance,stretch and fit. The improvement in crimp by the prebulking treatment isshown by a comparison with the same yarn drawn and treated by roll 34under the same conditions, except that the yarn is directly wound afterleaving the draw roll for the last time, without being prebulked bychamber 38. A segment of this latter yarn, removed from the bobbin andplaced in boiling water, forms a closely packed helix with radius R of0.21 millimeter. This corresponds to a length S of 1.32 millimeter, or19.2 crimps per inch. Accordingly, the prebulking step increases thenumber of helical crimps per inch by about 55 percent.

EXAMPLE III Nylon terpolymer is formed from 50 mols of hexamethylenediamine, 35 mols of adipic acid, 5 mols of terephthalic acid, and 10mols of isophthalic acid. The polymer is spun as a monofilament yarn,and then drawn at a draw ratio of 3.51 to a draw denier of 13.9, passingunder roll34 at 1,275 feet per minute. Roll 34 has a surface temperatureof 240 C., as compared to the terpolymer melting point of 220 C. Theyarn is then passed through prebulking chamber 38 and subjected to hotair at C. for a distance of 10 inches. About 3 pounds of air per hourare supplied at 3 p. s.

i. g. to chamber 38. Nip rolls 40 are driven at one-third the speed ofrolls 36, to insure substantially zero tension on the yarn in chamber38. A sample of this yarn withdrawn from the bobbin and relaxed inboiling water forms a helix with a radius R of 0.112 millimeter and apitch P of 0.333 millimeter. These dimensions correspond to a helicalcoil length S of 0.775 millimeter, or 32.6 helical crimps per inch offilament measured along the helix. The ratio of S/r is 37.2, and theboiling water shrinkage is 26 percent for drawn yarn from this polymer.

Seamless hosiery knit from the resulting yarn has excellent appearancedue to the high degree of crimp obtained. This particular yarn, however,has low tensile recovery which results in inadequate stretch recovery ofthe knit hose. The yarn is suitable for knit sheer scarves. Theimprovement in bulk by the prebulking treatment is shown by a comparisonwith the same yarn drawn and treated by roll 34 under the sameconditions, except that the yarn is directly wound after leaving thedraw-roll for the last time, without being prebulked by chamber 38. Asegment of this latter yarn, removed from the bobbin and placed inboiling water, forms a closely coiled helix with a radius of 0.15millimeter. This corresponds to a length S of 0.942 millimeter, or 27crimps per inch. Accordingly, the number of helical crimps per inch isincreased by approximately 21 percent by the prebulking step.

Nearly comparable improvement in final bulking level can be obtained ifthe latently bulked yarn is prebulked after winding in a separateoperation, if the prebulking operation is performed promptly. That is,the latently bulked yarn can be initially wound, then unwound and fedunder substantially zero tension through the prebulking chamber as aseparate operation. However, the effectiveness of the prebulkingdecreases as a function of the time during which the latent bulked yarnis subjected to tension before prebulking. For a substantial improvementin bulking level, the prebulking should therefore be performed in lessthan 2 days after the latent bulk is imparted to the yarn, with bestresults being obtained if the prebulking is performed before thelatent-bulked yarn is wound, as illustrated.

The prebulking medium can be hot air, steam,'or radiant heat. Polymerboiling water shrinkage as used herein is determined by drawing afilament to at least three times the spun length and measuring the drawnfilament length before and after immersion of the filament in boilingwater for 2 minutes. The shrinkage is the reduction in length divided bythe original drawn length immediately before immersion in water. Theterm homogeneous is used herein as opposed to conjugate, and includeshomopolymers and random or ordered copolymers, etc.

We claim:

1. A process for making a stretch yarn, comprising A. drawing a spunyarn at a given drawing tension to a length at least three times thelength of said spun yarn, to thereby provide a drawn yarn, said spunyarn being so selected that said drawn yarn has a boiling watershrinkage of at least 17 percent;

B. imparting latent crimp to said drawn yarn by heating one sidethereof, while said drawn yarn is under at least 50 percent of saiddrawing tension, to a temperature above the melting point of the yarnwhile keeping the opposite side of said drawn yarn below C;

C. feeding said yarn at a given speed to a treatment zone;

D. prebulking said yarn by subjecting said yarn in said treatment zoneto a temperature above the glass transition temperature of said yarnwhile said yarn is under substantially no tension;

E. withdrawing said yarn from said treating zone at a speed between 30and 60 percent of said given speed; and

F. collecting said yarn in an orderly fashion.

2. The process defined in claim 1, wherein said step of prebulking isperformed before said drawn yarn is collected.

1. A process for making a stretch yarn, comprising A. drawing a spunyarn at a given drawing tension to a length at least three times thelength of said spun yarn, to thereby provide a drawn yarn, said spunyarn being so selected that said drawn yarn has a boiling watershrinkage of at least 17 percent; B. imparting latent crimp to saiddrawn yarn by heating one side thereof, while said drawn yarn is underat least 50 percent of said drawing tension, to a temperature above themelting point of the yarn while keeping the opposite side of said drawnyarn below 100* C; C. feeding said yarn at a given speed to a treatmentzone; D. prebulking said yarn by subjecting said yarn in said treatmentzone to a temperature above the glass transition temperature of saidyarn while said yarn is under substantially no tension; E. withdrawingsaid yarn from said treating zone at a speed between 30 and 60 percentof said given speed; and F. collecting said yarn in an orderly fashion.2. The process defined in claim 1, wherein said step of prebulking isperformed before said drawn yarn is collected.